Development of Thinnest Wall Catalyst Substrate 2002-01-0358
The thinnest wall thickness of automotive catalyst substrates has previously been 30 μm for metal substrates and 50 μm for ceramic substrates. This paper describes a newly developed catalyst substrate that is the world's first to achieve 20-μm-thick cell walls. This catalyst substrate features low thermal capacity and low pressure loss.
Generally, a thinner cell wall decreases substrate strength and heat shock resistance. However, the development of a “diffused junction method”, replacing the previous “wax bonding method”, and a small waved foil has overcome these problems. This diffused junction method made it possible to strengthen the contact points between the inner waved foil and the rolled foil compared with previous substrates. It was also found that heat shock resistance at high temperature can be much improved by applying a slight wave to the foil instead of using a plane foil.
As a result of these investigations, we were able to produce a practical high-performance catalyst substrate that has low thermal capacity, low pressure loss, excellent strength and good heat resistance. This newly developed metal substrate with 20-μm-thick walls facilitates a faster catalyst light-off characteristic and reduces cold-start HC emissions by 20% compared with the performance of a metal substrate that previously had the thinnest walls of 30 μm. It has been difficult to reduce cold-start HC emissions of turbocharged V6 engines, because their exhaust gas temperature is lower than that of naturally aspirated engines. Nonetheless, the use of the new substrate for the close-coupled catalyst together with an underfloor HC trap catalyst achieves low HC emission levels without any loss of engine output or increase in the usage of precious metals.